Valve drives with a lever-type cam follower, whose pivot bearing is displaceable for generating a variable opening lift of the gas-exchange valve on a circular arc, are known in the state of the art. In EP 0 717 174 A1, which is considered as a class-forming invention, a valve drive with a rocker lever is shown, whose rocker-lever axis is displaceable on a circular arc concentric with the center axis of the camshaft. According to FIG. 3 of this publication, the changing kinematic relationships of the valve drive in the transfer of the raised section of the cam to the gas-exchange valve lead not only to a variable maximum lift of the gas-exchange valves, but also to a considerable shift in its control times, i.e., the opening and closing times of the gas-exchange valve with reference to the angular position of the cam or crankshaft.
A change to the control times and the maximum lift that is not independent of each other, however, can be undesirable for several reasons. The internal combustion engine is operated, for example, at an operating point close to idling, in which the residual gas content is to be minimized with reference to the smooth running of the internal combustion engine, typically with small valve overlap between the inlet and outlet valves, as well as with a small maximum lift. In contrast, in the partial load region, greater valve overlap for the residual gas preparation is advantageous from exhaust-gas emission and fuel consumption reasons, while, however, the maximum lift of the gas-exchange valve is to remain essentially unchanged relative to the maximum lift set during idling.
Another disadvantageous aspect of the mentioned dependency is also to be seen in that the direction of the control time shift is dependent on the rotational direction of the camshaft. For internal combustion engines in a V-arrangement and mirror-symmetric valve drives, this can have the undesired effect that the control times of gas-exchange valves of one cylinder bank are shifted with decreasing maximum lift in the direction of a retarded camshaft angle and the gas-exchange valves of the other cylinder bank are shifted with decreasing maximum lift simultaneously in the direction of an advanced camshaft angle. The synchronization of the control times for the two cylinder banks then absolutely necessary for the operation of the internal combustion engine would basically be possible through an overlapped angular adjustment of one or two camshafts, for example, through the use of a camshaft adjuster, would require, however, an exceptionally large adjustment range of the camshaft adjuster that can be reduced to practice only with difficulty due to the considerable and opposite control time shifts.